Cassini snaps weird hexagon on Saturn

Emma Woollacott, 10th December 2009

After waiting years for the sun to rise on Saturn's north pole, NASA's Cassini spacecraft has detailed pictures of the bizarre hexagon which frames it.

The hexagon is created by a jet stream flowing around the north pole at about 220 miles per hour.

The last visible-light images of the entire hexagon were taken nearly 30 years ago - the last time spring began on Saturn. But the light faded, and the north pole was in darkness for 15 years.

Now, much to the delight and bafflement of Cassini scientists, the location and shape of the hexagon in the latest images match up with what they saw in the Voyager pictures.

"The longevity of the hexagon makes this something special, given that weather on Earth lasts on the order of weeks," said Kunio Sayanagi, a Cassini imaging team associate at the California Institute of Technology. "It's a mystery on par with the strange weather conditions that give rise to the long-lived Great Red Spot of Jupiter."

Scientists are still trying to figure out what causes the hexagon, where it gets and expels its energy and how it has stayed so organized for so long.

They plan to search the new images for clues, taking an especially close look at the newly-identified waves that radiate from the corners of the hexagon - where the jet takes its hardest turns - and the multi-walled structure that extends to the top of Saturn's cloud layer in each of the hexagon's six sides.

Scientists are also particularly intrigued by a large dark spot that appeared in a different position in a previous infrared image from Cassini. In the latest images, the spot appears in the 2 o'clock position.

"Now that we can see undulations and circular features instead of blobs in the hexagon, we can start trying to solve some of the unanswered questions about one of the most bizarre things we've ever seen in the solar system," Baines said. "Solving these unanswered questions about the hexagon will help us answer basic questions about weather that we're still asking about our own planet."